To obtain new insights into the ways in which multigene families arise, diverge, and their genes are differentially controlled, I propose to study the genetic history of the haptoglobin gene family and the evolution of the differential control of its genes in primates and humans. The haptoglobin gene cluster is an excellent model system for this overall goal for the following reasons. In humans the cluster has two genes; an apparently functional but unexpressed haptoglobin-related gene (Hpr) occurs at 2.2 kb downstream of the expressed haptoglobin gene (Hp). In the first intron of Hpr there is a novel retrovirus-like sequence, RTVL-I. Gene duplications, unequal crossing-overs, gene conversions and insertions of foreign sequences have been observed in the cluster. The haptoglobin gene family has changed rapidly in recent primate evolution: it has one member in new world monkeys, three members in old world monkeys and apes, and two members in humans. Yet it is still sufficiently simple that one can hope to detect and decipher complete details of the genetic events which have taken place during its recent evolution. Specifically, (1) I will clone the haptoglobin genes in primates (spider monkey, rhesus monkey and chimpanzee) to analyze the genetic events associated with changes in the number of haptoglobin genes in primates. (2) I will investigate examples of variants in the human haptoglobin gene cluster in which the number of genes is changed or the level of expression of a gene is altered. (3) I will investigate the cause of the apparent nonexpression of the Hpr gene by studying the expression of the Hp and Hpr genes and of the RTVL-I element in human hepatoma cells known to secrete haptoglobin. The methylation pattern of the haptoglobin cluster, and stable messages and nuclear transcripts will be assayed. The effects of the RTVL-I element on the transient expression of Hp and Hpr will also be investigated in various hybrid plasmids. (4) The in vivo expression of the haptoglobin gene family in primates will be studied with emphasis on rhesus monkey. (5) The nucleotide sequence of the RTVL-I element in the Hpr gene will be completed.